Electrical communication cable



Dec. 23, 1952 E. w. SMITH 2,623,093

ELECTRICAL COMMUNICATION CABLE I Filed May 5, 1949 souo POLYETHYLENE.LAYER-6 CONDUCTOR INSULATION\7 (/y cououcfoflsg IOBSTEEL AMOURING TAP:

POLYETHYLENE TAPE; {g on,

jl UXILIARY TWIN CORE 615m :zsquencv can con:

' comuc-nye TAPE IENTRAL cououc-roa INVEN OR Patented Dec. 23 1952England,- assignor to Canada -Wire and Cable Company Limited, Leaside;Ontario; Canada, a

s..c.umqr tion 1- ;.rnliae ion Maxfii wie aeri 9 .55

tr 1n Great-BritaingMay: 2311948 -ill -zlgflfi) .1=1lThisinvention:relatesato communication$85215 and is concerned moresparticularly with multixxcore-cablesl capable *of, :car-rying a:- largeflnu bv 1:01"::telephone; :circuits :or; .a smaller number 10f broadcastor television circuitsandincorporating- 318,150 auxiliary pairs; or"quads? for-supervisin attended-.repeaters.

.Thexinventionghas for its object to provide a multiecore-gcablezof: ths til-1 .8 whichawillab ihigh ;:efficient ,electrically-b utwhich. willbe relatively cheapto manufacture and install, lightin weight-.:and";1mafiected; by mo,isture; sowthat it? can "be plaid in waterloedeor damp;- locations.

- In the past, cablesof-this type have-been made up :of .two :or more;-tubu;lar gcoaxial cores' of, airsnacedeconstructionwithanQuter:conductorlw .sisting; of a :plurality ;of long-lay coppertapes,

q-preterably interlocking or a single longitudinal.

tape bent to form a cylinder with a; longitudinal butt-joint, ,and'thesecoaxialcores have been laid up with a number (e. g. twelve) of ordinarypaper insulated telephone nuadsz-fonservicing the repeater'. stations thr omnosite ,cable. ins finally. lead sheathed overall toprovide-"security against ingress of moisture. It will be apparent thatsuch constructions are "extremely heavy and that ingressofymoisture, dueionexample to mechanical damage ,ofytheleadsheath-wouldquicklylead; tothe waterlogging of the entire -system and; interi ruptionof;.transmission.

",flhe-inventionbroadly stated r-resides iii-employing injtheicable,insulating; terials which-ere :both, extremely goodwdielectrics; andalso substantially impervious to, water, thushenabling the use of a leadsheath to be'eliminate'd'and economizing in bothweight and cost.

' According to the presentiinvention thes-cores in the communicationcable comprise a central con- 1 ductor, anintermediate layer-of:solidinsulation -*material,*-an outer conductorconsisting-"of-aconductive tape applied-longitudinally over the solidinsulation with its edges overlapping and secured in position by aconductive tape applied helically over thelongitudinal tape and an outerthermoplastic sheath applied over said outer tape, said solid insulationlayer consisting of polyethylene or a material having substantiallysimilar dielectric characteristics and resistance to water penetration.

In accordance with one feature of the present invention a coaxial corefor use in a communication cable of the type referred to consists of acentral conductor separated by a solid thermoplastic water-resistantdielectric from an outer v conductor composed of a single. conductivetape .--:anplie.d lensitudinallyhwiths a bs an i re nandboudzin;position b a sho tv ay co u eritapew applied w t ve pp n e rwth.whol bein cov red y a app 0f w r-r ,rsistant nQ -.meta1 :tap

In accordance with another feature of the irryentiona multi-corecommunication cable of the type referred :to comprises a number(preferably t:w0 ;or our) of eoaxial cores aslset out above laid upwithaplurality of-twisted twin or quad cables r-providiyngwrepeatersupervisory and control cir- .cuits,;the conductors of such twins orquads beineinsulated-wltha solid thermoplastic and -water,resistantdielectric, and the whole being ziilledlcircular and served with jute orother contventionalmaterial, lightly armoured with steel tape;and-;finally covered with compounded fabric tapes or jute yarn.

:E eier bl c t 11 35 q a t of sin le .s and conductorsinsulated withdielectric ma- .,-terial ,;col oured as required -for identification,,"twistedtogether and filled circular with a simislar. dielectric. and.advanta ou .z e e I s y --:th e tsu h. pairs. rgqua s. a e- 11p t th-r.-s .iaszto 011m. azcpn enic t a s m i lay timthe-i rstices. b twee 1he c0 x lw fIfh iadectriema er li m o d th oue out s npreferably/polyethyleneor a mixture thereof. with yothenmaterialssuch,as-polyisobutylene, but the {301;8S50f'517h6 signal pairs may insome cases be insulatedwwith, va lower grade of water-resistantdielectric, :such as polyvinyl chloride or similar compounds.

* The invention is illustrated in the-accompany- 35. =ing drawing whichis aperspective. sectional view --wot-.wacommunication cable having four-co-axial scores: laid up; with-twin cables.

--..Referring tothe drawing; the cable comprises .v four co-axial typecable coreseach indicated generally rat C-laid up with. twin cablesindicated at -T,c-of-whichl=there are-fiver one being (central and theremainder spaced in the recesses between adjacent cores C.

Each core C comprises a central conductor l enclosed in a solid layer 2of insulation consisting of a thermoplastic water-resistant dielectric.Applied to the insulation layer 2 is a single conductive tape 3, whichis wrapped longitudinally about the core so formed, with its edgesoverlapping and held in position by a metal tape 4, the latter beingwound over the conductor 3 with a short lay and applied with overlappingedges. The whole is then finally covered with insulation tape 5. Thedielectric used in the composition or the insulation layer 2 and of thetape preferably consists of polyethylene. In the embodiment shown eachtwin cable T consists of two cores 6, 6, of plain copper wire coveredwith a laper of insulation 1 also preferably of polyethylene and unitedin an outer covering of insulation 8 also of polyethylene. The fOlllcores C and five twin cables T are laid up in the positions shown andenclosed in a jute bedding 9 over which are wound steel armouring tapesIll, the whole being finally enclosed in an outer jute serving l I.

An example of a two core cable in accordance with the inventioncomprises two'coaxial cores each of which consists of a singleconductor, e. g. 0.096" plain copper wire, insulated with polyethyleneto a diameter of 0.350". The coaxial return conductor is a single coppertape, ap

proximately 1.3" x 0010". applied longitudinally with an overlap ofapproximately 50%, and may be crimped. transversely at intervals toenhance its flexibility. This return conductor is bound down by means ofa single copper tape applied with a short lay and a overlap followed bya polyethylene tape likewise applied with a short lay and a 20% overlap,the overall size of each co-axial core being approximately 0.407".

The signal pairs for supervising and controlling the repeaters in a twocore cable are made up of two cores each comprising a small plain copperwire, 0.028 in diameter, covered with a solid insulation of polyethylene(coloured as required) to 0.068". Two such cores are twisted togetherand then filled circular and belted with polyethylene to a diameter of0.152. Three such pairs are then laid up together with a lay opposite tothat of the individual pairs to give a six-core assembly having anoverall diameter of approximately 0.32.

Laid up with the two coaxial cores, with their outer surfaces incontact, are two groups of three signal pairs and jute wormings toproduce a circular form. This assembly is then served with cutched juteyarn and armoured with two steel tapes applied helically with a 50% gapand breaking joint so as to provide a closed armour layer. The cable isfinished off by applying two compounded Hessian tapes to give somedegree of protection to the steel tapes. The overall diameterof thefinished cable is of the order 1.33".

Each of the two coaxial cores constructed as described has a highfrequency impedance of approximately 52 ohms and an attenuation at 1.05mc/sec. of approximately 4 db/km. Assuming, therefore, an attenuationlimit of 40 db, the repeater spacing will be approximately 10 km. andsince the estimated near-end cross talk is better than 85 db at 60kc./sec. a pair of such coaxials will provide 240 telephone circuits.Each telephone channel occupies a frequency band of 4 kc./sec. and thechannels are packed closely together in the frequency spectrum, but each4 super-group of 60 circuits is separated by a small gap. The 240circuits are assemblied in four super-groups covering the frequencyrange 60 to 1052 kc./sec. with the "go channels in one coaxial and the"return channels in the other.

Obviously, by reducing the repeater spacing it is possible toaccommodate a greater number of telephone circuits. For example, with arepeater spacing of 6.5 km. ten supergroups can be accommodated, giving600 circuits per pair of coaxial cores in the frequency range 60 to 2540kc./sec., at which higher frequency the attenuation is approximately 6db/km.

It will be understood that the signal pairs are employed only forsupervisory and control purposes in connection with the repeaters, whichmay be at unattended stations and be fed with power via the innerconductors of the coaxials.

I claim:

A multi-core high frequency land communication cable, comprising incombination a plurality of high frequency co-axial cores, each co-axialcore comprising a central conductor, a solid layer of polyethyleneenclosing the conductor, an outer conductor comprising a firstconductive tape applied longitudinally over'the polyethylen layer withan overlap along its edges and a second conductive tape wrapped with ashort lay over the first conductivetape, and a layer of electricalinsulation comprising a polyethylene tape applied helically over thesecond conductive tape; a plurality of auxiliary cores laid up in theinterstices between the co-axial cores, each of the auxiliary corescomprising a conductor and a solid layer of polyethylene enclosing theconductor; an insulating bedding in which the cores are embedded; aprotective armouring tape over the bedding; and an insulating servingenclosing the armouring tape.

ESMOND WASSELL SMITH.

REFERENCES CITED I The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Great Britain Nov. 13, 1945

